Rationale The inter-individual pain experience immediately after surgery is considerable. In addition, a number of patients develop chronic post surgery pain (CPSP). Patients undergoing surgery for breast cancer are at risk of developing both acute post surgical pain as well as CPSP. Recently, in a group of patients with chronic back pain, it was demonstrated how subjectively reported pain is associated with specific electroencephalography (EEG) parameters, namely the N2 and P3 components of the pain event-related potential (ERP). It was concluded that ERP was associated with self-reported pain in daily life up to two weeks after the measurement. This resulted in the current hypothesis that EEG may be a predictor for postoperative pain.

Study design Prospective cohort study. Within 2 weeks before surgery, 150 patients will undergo an EEG measurement with five 'vulnerability' tasks. The experiment will be repeated 6 months postoperatively.

Study population: Female patients with breast cancer who will undergo breast surgery, between the ages of 18 to 65 years.

Main study parameters/endpoints Primary outcome is postoperative pain, measured in a pain diary 4 days postoperatively. Secondary outcomes are development of chronic post surgery pain and quality of life. The main goal is to develop a comprehensive prediction model for acute and chronic postoperative pain after breast cancer surgery, based on the EEG results of the five vulnerability experiments.

Chronic pain (>3months) with an average severity of at least a VAS score 4 during the last two weeks.

Chronic pain for which invasive treatment is needed.

Use of (weak / strong) opioids in the last week.

A history of opioid addiction.

Regular use of the following medications in the last year:

antiepileptics,antipsychotics and anxiolytics.

ASA 3 or higher.

Consumption of alcohol (>4 units) and / or drugs the evening before.

Alcohol consumption (>= 5 units/day).

Illiteracy, problems with self expression, language barrier.

Serious vision and / or hearing problems, interfering the performance of the experimental tasks.

A history of psychiatric complaints and/or epilepsy .

A medical history of CVA or TIA.

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Please refer to this study by its ClinicalTrials.gov identifier: NCT01392248